Peppercorn-sized clusters of human brain cells grown in a laboratory for a record seven years have aged in a way similar to the brain cells inside the human body, according to scientists.
The tiny clusters, known as organoids, are grown from stem cells and are used by researchers around the world to study how the brain develops and to test new medicines without using animals such as mice.
Most organoids survive only for a few months, which limits them to showing the earliest stages of brain development. Human brains, by contrast, take nearly 20 years to fully mature.
In this study, a US-led research team kept some organoids alive for around seven years, making them the oldest ever grown, said Paola Arlotta, the senior author of the study.
Researchers found that the organoids continued to develop and mature over the years, even though they had never been inside an embryo or a body.
Arlotta, a Harvard University professor, said the findings show that the brain can continue developing outside the human body for an unprecedented period.
The study, published in Nature, said the organoids “recorded the passage of time and retain a memory of the developmental steps already performed.”
Arlotta stressed that this does not mean the organoids have memories in the human sense. Instead, their earlier development is preserved at a cellular level.
She described organoids as biological models of human brain cells that are much less complex than a real brain and do not receive sensory input. Scientists generally agree that they are not capable of consciousness or higher brain functions.
The researchers studied the ageing organoids using three recently developed genetic clocks that estimate the biological age of cells. All three showed that the organoids changed over time in ways similar to normal brain cells.
To confirm their findings, the scientists also carried out what Arlotta called a “crazy experiment.” They mixed cells that had been developing for a year with cells that were only two weeks old, creating a chimera.
The younger cells behaved normally, but the older cells moved ahead in development and began producing neurons that usually take around four months to form.
Arlotta said the experiment effectively “warped time” for brain development and could one day help speed up the study of certain brain cells.
The previous record for the oldest brain organoids was a little under two years.
Unlike the brains inside our heads, these lab-grown organoids do not have a body that can become ill or die. Arlotta said nobody knows whether they could theoretically outlive humans, though she suspects they may last a little longer.
The organoids used in the new research have since been destroyed.
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